The present invention relates to an oscillating hauloff device for removing a blown film from an extruding apparatus.
Oscillating haul-offs for removing a blown film from an extruding apparatus have been known for some time. The major design configuration that has been commercially successful for many years is an oscillating hauloff produced by the Windmoeller and Hoelscher (W&H).
Following extrusion of blown film, the film typically is in the form of a bubble. The sides of the bubble are then forced together when they reach nip rolls in the hauloff device. As the bubble is passed through the nip rolls, thickness variations exist around the circumference of the bubble. If this film is wound directly onto a roll, the thicker areas will cause the wound roll to build up faster than the thinner areas, creating hills and valleys on the wound roll surface. A major problem arises when such rolls are taken from the extrusion process and subsequently unwound and conveyed through converting equipment such as printing presses, laminators or bag machines.
Uneven rolls considerably reduce the speed of this equipment and the quality of finished product. The unevenness of the roll causes slack in some areas of the film and tightness in other areas which ultimately causes creases in the film web. On the printing press, for example, the ink will not transfer to the film inside of a crease which degrades product quality. These manufacturing processes have to use spreader rolls or other means in an attempt to eliminate these creases. These additional processing steps complicate and slowdown the process.
In other downstream equipment, the bag machine has several nip rolls in order to draw the film into the sealing and/or punching area. When the film is drawn through these nips rolls any slack area will result in further creases. If the crease happens to be in a location where a seal is placed, that seal will be defective.
In all cases, the better the roll quality coming from the extrusion line, the faster one can run the downstream equipment and the probability is increased of producing a better quality product. While the need for improved roll quality has been recognized for some time and there have been several attempts at solving it, these attempts still have a number of deficiencies.
An initial attempt to solve the quality problem utilized a vertical design oscillating hauloff. This device had a significant vertical height requirement; the wider the film, the taller is the oscillating hauloff and the taller is the required building to house it.
Another problem with the vertical design, is that the film has to go around several vertical idler rolls which act as an accumulator as the unit rotationally oscillates. As film accumulates, overall output speed slows because some of the film's speed is taken up by the accumulation. The reverse happens when the unit reverses direction, line speed increases. This results in a variation in line speed that can cause film walking in the winder which degrades roll quality.
Other problems associated with subsequent prior art devices include the stability of the unit. One type of oscillating hauloff unit consisted of a frame having a small diameter shaft suspended from the center. It had horizontally mounted idler rolls and turning bars which turned at angles to one another to effect web direction corrections. The whole oscillating hauloff unit including all the idler rolls and turning bars as well as the nip rolls and collapsing frame were suspended from this single shaft. Any touching of the unit during operation caused it to swing resulting in film wandering and wrinkling. This single shaft also limited the size and location of auxiliary equipment such as air collapsing frames and associated blowers that could be suspended under the oscillating hauloff. Even if the extra weight could be handled, the support shaft would bend and cause misalignment if the load was not equally balanced. Such a machine would not be applicable or would have substantial drawbacks if applied to extrusion lines oriented to extrude the film downwardly.
Another problem which has occurred in prior art devices is uncontrolled wandering of the film. In horizontal designs, there have been two turning bars which work together to allow for a total oscillation of 360 degrees. As with any turning bar, frictional forces cause a slight shift in axial position as the film passes around its diameter. This is in addition to the pure geometrical shift associated with its diameter. It is well understood that the geometrical shift can be negated by properly offsetting the turning bar from the center of rotation. However, the wandering due to frictional effects has not been corrected and wrinkles have been induced. The result is that although normal process gauge variations are spread evenly over the surface of the wound roll, the wrinkles and associated creases due to wandering are wound into the finished roll.
Yet another problem of prior art devices is that the turning bars can be permanently deformed by deflection. This is because turning bars are hollow and lack sufficient rigidity due to the many air outlet holes in their surface, and thus, over time, forces exerted by the film have deformed the bars.
Another problem is related to the method for distributing utilities such as electrical power, water and other pressurized fluids (typically air) that are required during operation of the oscillating hauloff device. Utilities are fed to auxiliary equipment mounted within the moving structure of the oscillating hauloff using a long umbilical cord which is folded back and forth while wrapping around the unit .+-.180.degree. as the unit cycles. This folding motion stresses the wires and hoses as they flex and causes long term problems with breakage.